High temperature cement



Feb. 25, 1969 A. A. KELLAR ETAL 3,429,759

HIGH TEMPERATURE CEMENT Filed June 1'7, 1963 B. CARTER INVENTORS ARNOLDA. KELLAR MORRIS ATTOR United States Patent 3,429,759 HIGH TEMPERATURECEMENT Arnold A. Kellar and Morris B. Carter, Lawrenceburg,

Tenn., assignors to Union Carbide Corporation, a corporation of New YorkFiled June 17, 1963, Ser. No. 290,576

U.S. Cl. 156--155 4 Claims Int. Cl. C09j 3/00 This invention relates toa cement for joining carbonaceous articles, and more particularly, to acement which retains its joint strength at high temperatures.

Carbonaceous shapes are often assembled by bonding a plurality ofcarbonaceous segments together. When the thus assembled shapes areintended for use in high temperature applications such as in rocketnozzles or as nose cones, the bonding medium must retain itseffectiveness at high temperatures. In addition, such carbonaceousshapes generally are fabricated from graphite material which ischaracterized by a high density and low porosity. The bonding medium forsuch shapes cannot therefore rely on porosity in the graphite to providea gripping surface.

Accordingly, the principal object of the invention is to provide acement which retains its joint strength over the temperature range ofroom temperature to 3000" C. and above.

Another object of the invention is to provide high temperature cementwhich is suitable for use 'with high density graphites, such aspyrolytic graphite.

Broadly stated, the objects of the invention are accomplished by acement which comprises finely divided titanium diboride particles whichare bonded together by a carbonizable binder.

Among the many carbonizable binders which are suitable for use in thepractice of the invention are coal tar pitch, petroleum pitch, phenolformaldehyde resins and sugar. The preferred binder is a mixture whichcomprises 25 percent by weight furfural, 25 percent by weight furfurylalcohol, and 50 percent by weight phenol formaldehyde. The preferredconcentration range of this binder is 40 to 60 parts by weight binderper 100 parts by Weight titanium diboride.

The size of the titanium diboride particles is critical to the successof the invention and in order to obtain satisfactory cement all theparticles must be finer than 200 Tyler mesh, i.e. all through a 74micron screen opening. However, an average particle size below about 4microns should be avoided since such extremely small particles allow thejoint to be so thin that the carbonaceous binder is depleted bydispersion into the surface of the members to be joined.

In addition, stearic acid in a range of up to 5 parts by weight per 100parts by weight of titanium diboride may be optionally added to thecement. Stearic acid is immiscible with furfural and furfuryl alcoholand it imparts permeability to the cement during the curing step bysweating out of the cement and leaving pores. Other materials suitablefor this purpose are petroleum base greases, oils and other liquifiablematerial which is immiscible with furfural and furfuryl alcohol, such asparaffin.

Carbon or graphite segments may be joined by the cement of the inventionin either of two ways. The surfaces to be cemented may be either groundor not ground, the only requirement being that they are reasonably flatand parallel to one another. In addition, the best results are alsoobtained if the surfaces are moisture free.

In one method, the surfaces to be joined are coated with the cement andthen they are clamped together under pressure to form a thin joint. Thecement in the joint is then cured. The exact curing temperature and timePatented Feb. 25, 1969 ice varies with the particular binder which isemployed and with the size of the joint. The best time and temperaturefor a specific binder and size will be readily apparent to one skilledin the art.

After curing, the article resulting from the joined segments may bemachined or otherwise worked upon and is ready for applications at hightemperatures in excess of at least 2200 C. at any time.

In the second method, after curing as above, the joint is heated in aninert atmosphere to a temperature in excess of at least about 2200 C.prior to its ultimate use at such temperatures.

In either event, when the joined article is heated to temperatures inexcess of 2200 C. :50 C., the titanium diboride which is liquid at thistemperature dissolves the graphite at the interface of the joinedsegments and the carbonizable substance in the binder (which is graphiteat this temperature). The thus formed solid solution forms an excellentbond upon cooling. Until such interaction between the titanium diborideand the graphite occurs, the binder in the cement alone impartssufficient bond strength to the joint so that the joined article may beworked upon.

The bond which is formed between the segments being joined by the abovediscussed interaction is clearly observable in the drawing wherein thesole figure is a photomicrograph which has been magnified times. In thephotomicrograph, the reference character A identifies pyrolytic graphiteand the reference character B identifies the reacted cement of theinvention.

Illustrative of the success of the cement of the invention is thefollowing:

A carbonizable cement embodying the invention was prepared by mixing 100parts by weight titanium diboride particles of a fineness through 200Tyler mesh, 47 parts by weight of the above-identified preferred binderand 2 parts by weight stearic acid. This mixture was applied to thesurfaces of a number of high density graphite pieces, pairs of whichwere pressed together to form about a 75, of an inch thick joint. Thecement which formed the joint was then cured to a temperature of C. in16 hours.

A portion of the thus joined members were then heated to a temperatureof 2750 C. to cause the titanium diboride-graphite reaction to occur.

The average flexural strengths for both the cured and the cured andheated joints were then determined by single point loading of a 1.25 cm.span at the following temperatures:

Flexural strength, p.s.i.

Temperature Cured and heated Cured It will be appreciated from the abovethat joints which are made by the cement of the invention have goodflexural strength over the entire range from room temperature to 2500 C.both with and without pre-heating to such temperatures.

A further test was made with a scale-down nozzle in a static firingstation. The nozzle was cut into eight segments and cemented with theabove thermosetting cement. After a cure of 16 hours to 120 C. thejoined nozzle was pre-heated to 2750" C. The nozzle was then installedin a 6 inch solid fuel motor and fired 72 seconds at 5500 F. and 1000p.s.i. After firing, the nozzle joints displayed excellent strength.Erosion rate was normal for the basic graphite grade.

The cement of the invention after being mixed should be usedimmediately, although it may be stored for up to 30 days underrefrigeration. The cement of the invention may be provided as a twocomponent composition, the binder and stearic acid or equivalent in onecontainer, and the titanium diboride in the other, to give a cement withan unlimited shelf life.

We claim:

1. A cement for joining pyrolytic carbon or graphite articles whichcomprises titanium diboride particles having a particle size of lessthan 74 microns and a carbonizable binder, said binder comprising 25weight percent furfural, 25 weight percent furfuryl alcohol and '50weight percent phenol formaldehyde and being present in a range of fromabout 40 to 60 parts by weight per 100 parts by Weight of said titaniumdiboride.

2. The cement of claim 1 wherein stearic acid in a range of up to 5parts by Weight per 100 parts by weight of titanium diboride is alsoadded.

3. A cement for joining carbon or graphite articles which comprises 100parts by Weight finely divided titanium diboride particles, saidparticles all being of a size of 74 microns or less with the averageparticle size being above 4 microns, 47 parts by weight carbonizablebinder which comprises 25 weight percent furfural, 25 weight percentfurfuryl alcohol and 50 weight percent phenol formaldehyde, and 2 partsby weight stearic acid.

4. A method for joining high density graphite segments which comprisespreparing a cement comprising particles of finely divided titaniumdiboride and a carbonizable binder, said binder capable of yielding bondforming carbon at temperatures of less than 2200 C. and being present ina range of from about to 60 parts by weight per 100 parts by weight ofsaid titanium diboride and said titanium diboride having a particle sizeof 74 microns or less, providing the segments to be joined with fiat,parallel and moisture free opposed surfaces, coating the surfaces to bejoined with said cement, clamping said segments together to form a thinjoint, curing said cement in said joint and subsequently heating saidcement in said joint to a temperature of at least about 22.00 C.

References Cited UNITED STATES PATENTS 2,992,960 7/1961 Leeg et al161-249 X 3,120,453 2/1964 Fitzer et a1 117217 3,132,979 5/1964Biekerdike et a1 156-89 3,140,967 7/1964 Kaufmann et a1 15691 3,165,8641/1965 Shulze 464 3,175,918 3/1965 McGahan et a1 10641 3,187,502 6/1965Stover 35.6

FOREIGN PATENTS 618,367 2/1949 Great Britain.

' EARL M. BERGERT, Primary Examiner.

C. B. COSBY, Assistant Examiner.

US. Cl. X.R.

4. A METHOD FOR JOINING HIGH DENSITY GRAPHITE SEGMENTS WHICH COMPRISESPREPARING A CEMENT COMPRISING PARTCLES OF FINELY DIVIDED TITANIUMDIBORIDE AND A CARBONIZABLE BINDER, SAID BINDER CAPABLE OF YIELDING BONDFORMING CARBON AT TEMPERATURS OF LESS THAN 2200*C. AND BEING PRESENT INA RANGE OF FROM ABOUT 40 TO 60 PARTS BY WEIGHT PER 100 PARTS BY WEIGHTOF SAID TITANIUM DIBORIDE AND SIAD TITANIUM DIBORIDE HAVING A PARTICLESIZE OF 74 MICRONS OR LESS, PROVIDING THE SEGMENTS TO BE JOINED WITHFLAT, PARALLEL AND MOSITURE FREE OPPOSED SURFACES, COATING THE SURFACETO BE JOINED WITH SAID CEMENT, CLAMPING SAID SEGMENTS TOGETHER TO FORM ATHIN JOINT, CURING SAID CEMENT IN SAID JOINT AND SUBSEQUENTLY HEATINGSAID CEMENT IN SAID JOINT TO A TEMPERATURE OF A LEAST ABOUT 2200*C.